Distances to the Supernova Remnants in the Inner Disk

Abstract

Context. Distance measurements of supernova remnants (SNRs) are essential and important. Accurate estimates of physical size, dust masses, and some other properties of SNRs depend critically on accurate distance measurements. However, the determination of SNR distances is still a tough task. Aims. Red clump stars (RCs) have a long history been used as standard candles. In this work, we take RCs as tracers to determine the distances to a large group of SNRs in the inner disk. Methods. We first select RC stars based on the near-infrared (IR) color-magnitude diagram (CMD). Then, the distance to and extinction of RC stars are calculated. To extend the measurable range of distance, we combine near-IR photometric data from the 2MASS survey with the deeper UKIDSS and VVV surveys. With the help of the Gaia parallaxes, we also remove contaminants including dwarfs and giants. Because an SN explosion compresses the surrounding interstellar medium, the SNR region would become denser and exhibit higher extinction than the surroundings. The distance of a SNR is then recognized by the position where the extinction and its gradient is higher than that of the ambient medium. Results. A total of 63 SNRs' distances in the Galactic inner disk are determined and divided into three Levels A, B, and C with decreasing reliability. The distances to 43 SNRs are well determined with reliability A or B. The diameters and dust masses of SNRs are estimated with the obtained distance and extinction.

The distances to molecular clouds in the fourth Galactic quadrant

“…To obtain the extinction and distance profile of the sightline toward a given molecular cloud using the RCs, we first determine an empirical track of RCs by linking all peaks of the colour histograms of the RC candidates in the individual magnitude bins from the (J´K S , K S ) CMD. Similar to the previous works (e.g., Gao et al 2009 andWang et al 2020), we check the CMD by naked eyes to achieve a rough stripe of RCs. The borders of the RC candidates are defined as two cubic polynomial function that fit seven points manually selected.…”

“…Shan et al (2018Shan et al ( , 2019 use RCs to map the 3D extinction distribution of the sightlines toward the supernova remnants in the first and fourth quadrants of the Galaxy and estimate distances of them with extinction values from the literature. Wang et al (2020) use RCs to estimate extinction distances of 63 molecular clouds and infer them to the distances of supernova remnants.…”